1. Field of the Invention
The present invention relates to methods and apparatus for subterranean well completion. In particular, the invention relates to the manufacture, operation and use of side pocket mandrel tools that accommodate a through-bore flow of cement and enhance a turbulent flow of well working fluid behind the cement wiper plug within the side pocket mandrel as the plug is driven past the mandrel.
2. Description of the Prior Art
Side pocket mandrels are special purpose tubing sections assembled along a production tubing string within a subterranean well for producing fluid such as crude petroleum and natural gas. These special purpose tube sections include relatively short cylindrical barrels (side pockets) in parallel axis alignment with the primary tubular bore axis but laterally off-set therefrom. These side pockets have a bore opening within the tube section interior and an aperture between the barrel interior and the exterior of the mandrel wall. These side pockets constitute receptacles for fluid flow control devices such as valves or property measuring instruments. In the case of valves, fluid flow from the tubing bore into the well annulus or vice versa is controlled.
By means of wireline suspension structures, valve elements may be placed in or removed from the side pockets without removing the tubing string from the well. These flow control options are of great value to well production managers.
Another aspect of well production control that is facilitated by side pocket mandrels is gas lifting. There are many petroleum reservoirs holding vast quantities of petroleum fluids having insufficient internal driving force to raise the native fluid to the surface. Because of the reservoir depth, traditional pumping is not an option. In these cases, the formation fluids may be extracted by means of gas lifting.
There are numerous gas lifting techniques but, in general, a compressible fluid such as nitrogen, carbon dioxide or an external source of natural gas is compressed into the well annulus and selectively admitted into the production tubing bore via side pocket valves. A pressure differential rising of the gas flow within the tubing bore to the surface may be exploited to aspirate a petroleum flow along with the lift gas or to drive a plug along the tubing bore having a column of liquid petroleum above the plug.
When a well is first opened, the reservoir may have sufficient internal driving energy to produce a commercially adequate flow of the formation fluid to the surface. In time, however, that internal energy source may be dissipated long before the reservoir value is depleted. Production experience may anticipate such production developments by positioning side pocket mandrels in the production tube long before the actual need for gas lifted production. When the need for gas lifting arises, the only downhole operations required to begin gas lifting are the wireline placement of the gas lift valve elements in the respective side pockets. When compared to the enterprise of withdrawing and returning several miles of production tubing or coil tubing in a well, wireline procedures are minimal.
Such considerations are more imperative in those cases in which much of the well bore remains uncased. Extremely deep or long, horizontal well bores are examples. For example, a long well bore may be completed with minimum casing length. Below the casing, the raw borehole remains uncased through the formation production face. Completion of the well may include a single “trip” placement of production tube with cross-over and cementing valves. The well annulus between the production tube and borehole wall is cemented above the production zone for isolation. Production flow from the production zone is opened by perforating the production tube and surrounding cement annulus.
Unfortunately, a single trip completion with side pocket mandrels for later gas lifting, for example, has not previously been an available option. Delivery of the cement slurry down the production tube bore unreasonably contaminates the internal labyrinth of the side pocket mandrel.
It is an object of the present invention therefore, to provide a side pocket mandrel that may be cleaned of cement before it sets.
Another object of the invention is a method of single trip well completion that includes pre-positionment of side pocket mandrels that will be operatively available for subsequent gas lift operation.
Also an object of the invention is an apparatus for scouring the flow bore of a side pocket mandrel of cement or other contaminant.